Ecosystems are the biological community of organisms as well as the physical components of a specific area. A biological community is all of the populations of different species that live in a certain environment. An ecosystem can be as large as an entire forest or as small as a clump of moss that provides a habitat for plants, microscopic invertebrates, and bacteria.

Ecosystems can be thought of and studied in various contexts. Ecologists often study the flow of energy through ecosystems. Another focus of study of ecosystems involves understanding the interactions between the organisms that live within a community. Finally, ecological researchers study the interactions between organisms and the physical environment.

There are several important types of ecosystems on Earth. These ecosystems are often defined by the amount of precipitation they receive and the typical temperatures that they experience. Some of the more important ecosystems are the tropical rain forest, desert, temperate forest, tundra, and savanna or grasslands. Common aquatic ecosystems include lakes, rivers, estuaries, coral reefs, kelp forests, the open ocean, and the deep ocean.

In the 1700s, the science of biology exploded with new discoveries. Swedish botanist Carl Linnaeus (1707–1778) developed a vast classification system for living things, still in use today. Scientific knowledge about life on Earth became detailed enough to allow a sense of how the web of life interacts.

Charles Darwin (1809–1882) furthered this sense of life as an interconnected web in the mid-nineteenth century, especially with his On the Origin of Species (1859). He argued that interactions with other living things are among the most important factors shaping the course of natural selection. Western thinkers were quickly learning to see living communities as self-interacting, self-shaping, and self-sustaining—the essence of “ecological” thought. The word “ecology” itself was coined about 1870 by German biologist and Darwin supporter Ernst Haeckel (1834–1919).

An ecosystem is the collection of organisms, or the biological community, that lives in a certain area as well as the physical components of the environment. The biological community includes all of the populations of animals, plants, fungi, and bacteria. A population is all the members of a certain species that live in a location. In terrestrial ecosystems, the physical environment includes the type and conditions of soil or rocky terrain, the general climatic conditions, the amount of precipitation, and the amount of sunlight available. In aquatic ecosystems, the physical environment includes the salinity, temperature, and acidity of the water, the amount of sunlight available, the amount of sedimentation in the water, the amount of nutrients dissolved in the water, and the type of substrate below the water.

The flow of energy through an ecosystem plays a key role in the stability and functioning of an ecosystem. With few exceptions, the energy for life originates with light energy from the sun. Plants convert this energy to chemical energy stored in carbohydrates through photosynthesis. Herbivores then consume the carbohydrates in plants and use the energy from the chemical bonds for growth and reproduction. Carnivores consume the herbivores and assimilate the energy stored in the chemical bonds of the herbivores. Finally, the carnivores die, and their organic remains are decomposed by bacteria and fungi. These decomposers use the stored chemical energy in organis’s chemical bonds and convert the organic material into inorganic material that plants require to perform photosynthesis. With each successive step in the food chain, or food web in complex ecosystems, energy is lost as heat to the environment. Approximately 10% of the energy harvested from the sun by plants gets passed on to the herbivores. Similarly, only 10% of the energy stored in the chemical bonds of the herbivores is passed to the carnivores. As a result, most ecosystems have significantly more plants, or primary producers, than predators.

Every organism in an ecosystem depends on many other organisms in order to grow and reproduce. In order to grow, organisms require food. Both the struggle to obtain food and the struggle to avoid becoming food are major goals of the biological interactions in ecosystems. Predation is the consumption of one species by another species. The predator is the species that consumes the prey. Predators have developed adaptations